From 6c4f596a9a1a2c0321f0ba1f231d8dc23ae41836 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Wed, 15 Mar 2023 16:26:36 +0900
Subject: [PATCH] Make osu! touch input aware of the distance travelled of a
 non-direct touch

---
 .../TestSceneOsuTouchInput.cs                 | 28 +++++++++++++++++++
 .../UI/OsuTouchInputMapper.cs                 | 18 ++++++++++--
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/osu.Game.Rulesets.Osu.Tests/TestSceneOsuTouchInput.cs b/osu.Game.Rulesets.Osu.Tests/TestSceneOsuTouchInput.cs
index 72bcec6045..bd32d820d1 100644
--- a/osu.Game.Rulesets.Osu.Tests/TestSceneOsuTouchInput.cs
+++ b/osu.Game.Rulesets.Osu.Tests/TestSceneOsuTouchInput.cs
@@ -150,6 +150,34 @@ namespace osu.Game.Rulesets.Osu.Tests
             assertKeyCounter(1, 1);
         }
 
+        [Test]
+        public void TestPositionalTrackingAfterLongDistanceTravelled()
+        {
+            // When a single touch has already travelled enough distance on screen, it should remain as the positional
+            // tracking touch until released (unless a direct touch occurs).
+
+            beginTouch(TouchSource.Touch1);
+
+            assertKeyCounter(1, 0);
+            checkPressed(OsuAction.LeftButton);
+            checkPosition(TouchSource.Touch1);
+
+            // cover some distance
+            beginTouch(TouchSource.Touch1, new Vector2(0));
+            beginTouch(TouchSource.Touch1, new Vector2(9999));
+            beginTouch(TouchSource.Touch1, new Vector2(0));
+            beginTouch(TouchSource.Touch1, new Vector2(9999));
+            beginTouch(TouchSource.Touch1);
+
+            beginTouch(TouchSource.Touch2);
+
+            assertKeyCounter(1, 1);
+            checkPressed(OsuAction.LeftButton);
+            checkPressed(OsuAction.RightButton);
+            // in this case, touch 2 should not become the positional tracking touch.
+            checkPosition(TouchSource.Touch1);
+        }
+
         [Test]
         public void TestPositionalInputUpdatesOnlyFromMostRecentTouch()
         {
diff --git a/osu.Game.Rulesets.Osu/UI/OsuTouchInputMapper.cs b/osu.Game.Rulesets.Osu/UI/OsuTouchInputMapper.cs
index 8df1c35b5c..76cb388949 100644
--- a/osu.Game.Rulesets.Osu/UI/OsuTouchInputMapper.cs
+++ b/osu.Game.Rulesets.Osu/UI/OsuTouchInputMapper.cs
@@ -97,8 +97,8 @@ namespace osu.Game.Rulesets.Osu.UI
                 return;
             }
 
-            // ..or if the current position tracking touch was not a direct touch (this one is debatable and may be change in the future, but it's the simplest way to handle)
-            if (!positionTrackingTouch.DirectTouch)
+            // ..or if the current position tracking touch was not a direct touch (and didn't travel across the screen too far).
+            if (!positionTrackingTouch.DirectTouch && positionTrackingTouch.DistanceTravelled < 200)
             {
                 positionTrackingTouch = newTouch;
                 return;
@@ -117,6 +117,12 @@ namespace osu.Game.Rulesets.Osu.UI
 
         private void handleTouchMovement(TouchEvent touchEvent)
         {
+            if (touchEvent is TouchMoveEvent moveEvent)
+            {
+                var trackedTouch = trackedTouches.Single(t => t.Source == touchEvent.Touch.Source);
+                trackedTouch.DistanceTravelled += moveEvent.Delta.Length;
+            }
+
             // Movement should only be tracked for the most recent touch.
             if (touchEvent.Touch.Source != positionTrackingTouch?.Source)
                 return;
@@ -148,8 +154,16 @@ namespace osu.Game.Rulesets.Osu.UI
 
             public OsuAction? Action;
 
+            /// <summary>
+            /// Whether the touch was on a hit circle receptor.
+            /// </summary>
             public readonly bool DirectTouch;
 
+            /// <summary>
+            /// The total distance on screen travelled by this touch.
+            /// </summary>
+            public double DistanceTravelled;
+
             public TrackedTouch(TouchSource source, OsuAction? action, bool directTouch)
             {
                 Source = source;